Steam power generating apparatus



April 28, 1959 s. M. ARNOW 2,883,832

STEAM POWER GENERATING APPARATUS Filed May :5, 195a WJTER- JEHL mwsmom Sam/eZMflr/ww, BY PM J PM A TTORNEYS United States Patent STEAM POWER GENERATING APPARATUS Samuel M. Arnow, Philadelphia, Pa.

Application May 3, 1956, Serial No. 582,471 14 Claims. (CI. 60-67) This invention relates to steam power generating apparatus, and more particularly to a steam power generating station in which turbines are utilized to drive electric generators, for example. In such plants the heat carried away by the combustion gases from the boilers represents one of the chief sources of efliciency loss.

It is an object of this invention to provide a steam power generating apparatus including an eflicient means for tempering incoming air.

Another object is to provide an efiicient steam power generating apparatus arranged for absorbing heat from exhaust gases, for preheating condensate, and for tempering incoming air, all in combination.

Still another object of this invention is to provide a steam boiler having an air preheater and which includes a readily controllable incoming air tempering means for introducing air at a substantially constant temperature to the preheater, notwithstanding fluctuations of temperature of the air introduced into the tempering means.

Another object is to provide an elficient means for utilizing hot exhaust gases for preheating the condensate at the most effective point in the steam power thermal cycle, without condensing ingredients of the exhaust gases or corroding the preheater.

Other objects and advantages of this invention, including the simplicity and economy of the same, and the ease with which it may be applied to existing steam power generating systems, will further become apparent hereinafter and in the drawing.

Referring to the drawing, the number 1 represents generally a boiler having a gas exit 2 connected through breeching 3 to a stack 4, the draft being induced by a blower or blowers designated 5. Combustion supporting air is introduced into the lower portion of the fire box of the boiler 1 by way of a duct 6 by action of a blower or blowers 7, said duct passing through the gas exit 2 of the boiler and having there interposed in it, a preheater 8 which absorbs some of the flue gas heat, and whereby the air is preheated before entering the boiler. Steam is conducted from the boiler 1 through a conventional pipe 9 to drive a turbine 10 having an associated condenser 11. Leading from different bleed points of the turbine 10 are pipes 12, 13 and 14 through which exhaust steam at different pressures is channelled to feedwater heaters 15, 16 and 17 respectively. For greatest economy of operation, the heater 17 should be connected to the bleed point nearest the exhaust of the turbine.

The condensate from the condenser 11 is propelled, by a plurality of pumps diagrammatically shown as a pump 18, through a feed pipe line 19 which extends to a coil 20 in the feedwater heater 17, then, in accordance with my invention, to a low level economizer 21 in the breeching 3. It should be understood that the coil 20, although conventionally referred to and illustrated as a coil, in practice is actually a system of tubes. It is further to be understood that a system of tubes well known in the art as used for heat transfer purposes,

will hereinafter be referred to for convenience as a coil. The feedwater pressure in economizer 21 should be above atmospheric, to prevent leakage of exhaust gases into the feedwater. Continuing on, the line 19 extends first to a coil 22 in the feedwater heater 16, then to a coil 23 in a feedwater heater 15, through a plurality of boiler feed pumps diagrammatically shown as a pump 25. From the pumps 25, line 19 extends through an economizer 26 (which latter is located within the boiler), and finally to the boiler 1 in which the line 19 terminates. An additional feedwater heater 27, or a group of them, may also be provided, respectively fed by ascending pressure bleed points.

An important feature of my invention is the provision in the air duct 6 of a water-to-air heat exchanger 30 which is set into the air inlet duct 6 and which is interposed in a closed water circulation pipe line 31. Pipe line 31 also includes a coil 32 located within the feedwater heater 17. The water in the line 31 is under positive pressure and circulated by a pump indicated at 33, such water being purified so that any possible leakage into the heater 17 would not contaminate the condensate. Also, since the water in line 31 is under positive pressure, there is no possibility of leakage of air into the line 31 at the air tempering heater 30 to contaminate the water. A conventional cascading system of heater condensate drains extends from heaters 27, 15, 16 and 17 back to condenser 11. This is a closed system sealed from the atmosphere, thus preventing air from entering heater 17. The rate of circulation is regulated by a temperatureresponsive valve 34 controlled by a thermostat 35 having its sensing element located within the air duct portion 36, which is downstream relative to the water-to-air heater 30. Valve 34 is downstream relative to the pump 33.

It is important to observe that the feedwater heater 17 is connected to transfer heat through both the coils 32 and 20. Working at sub-atmospheric pressure, at the bleed point of lowest possible pressure, the heater 17 is ideally suited economically for pre-heating the condensate prior to its introduction into the low level economizer 21, because the work done by the steam in the turbine'is at a maximum when bled off at this low pressure. Moreover, heat is concurrently transferred by heater 17 to the water in pipe 31, whereby both the low level economizer 21 and the tempering heater 30 are heated from a common, subatmospheric pressure source.

In operation, the temperature of the gases as they leave the air preheater of the conventional steam generating system is usually maintained at about 260 F., and the air entering the preheater is desirably not less than about F.; otherwise the flue gases leaving the preheater may be cooled below the dew-point and the maintenance cost of the preheater would become exces sive because of corrosion resulting from condensation. In order to avoid this difficulty, it is conventional to temper the air by increasing its temperature by about 60 F. before it enters the preheater. For 65 F. (annual average) incoming air, the temperature would be raised to about F. which is safely above the desired minimum. Steam is used for this purpose and usually is Withdrawn from one of the bleed points in the turbine. However, using this method it has not been found practical to control the extent of preheating. In conventional plants, in order to safeguard against contamination of the steam by the air, the bleed point selected must have a pressure above atmospheric pressure at all operating loads.

In accordance with the improved air preheating system provided by withdrawing the steam at the lowest pressure bleed point, which is below atmospheric pressure and in one practical case, for example, has a full load pressure of approximately 5.7 pounds per square inch absolute. Notwithstanding the fact that the steam is withdrawn at a pressure below atmospheric, steam contamination is nevertheless avoided. As was before indicated, the with drawal of the steam at such low pressure bleed pomt results in an increase in work done by the turbine before the steam is withdrawn.

An even greater gain in economy is achieved by causing the feedwater heating circuit to pick up heat from the flue gases just ahead of the stack. This heat, which includes the heat added by the induced draft fans would, in a conventional plant, normally be lost up the stack. This feature of this invention in the example cited above, permits dispensing with the feedwater heating bleed point 40 of the turbine, which in a conventional plant would be intermediate between bleed points 13 and 14 and connected. to an additional feedwater heater interposed betweenthe feedwater heaters 16 and i7, and thus increases the work done in the turbine by the steam which otherwise would have been extracted. It will be observed that the bleed point 40 which would be at a pressure of about 11 pounds per square inch absolute at full load, is shown blanked off. Under normal operating conditions, the bleed line 13 may be under a full load pressure of about 22 pounds per square inch absolute, while the bleed line 12 may be under about 54 pounds per square inch absolute at full load.

Although this invention has been shown and described with reference to one specific embodiment thereof, it will be appreciated that various modifications may be made without departing from the spirit or scope of this invention. For example, equivalent elements may be substituted for those shown in the drawings, parts may be reversed, and various features of the invention may be used independently of other features, all without departing from the spirit and scope of this invention as defined in the appended claims.

I claim:

1. In a steam power generating system including a boiler having an air intake means, a turbine driven by steam from said boiler, and a condenser connected to condense the steam from said turbine, said turbine having a plurality of steam bleed points of which at least one is below atmospheric pressure, the combination which comprises a subatmospheric pressure feedwater heater, means for carrying steam from said bleed point below atmospheric pressure to said feedwater heater, a low level economizer located in the path of flow of the boiler exhaust gases, means for pumping the condensed steam from the condenser through said feedwater heater and then at a pressure above atmospheric pressure through said low level economizer, a preheater arranged to transfer heat from exhaust gases to the incoming air, an air tempering heater located in the path of flow of incoming air ahead of said preheater, and separate water circulating means comprising a closed circuit sealed from fluid communication to said condensed steam and in heat conducting relation to said air tempering heater and to said feedwater heater for transferring heat from said feedwater heater to said air tempering heater.

2. In a steam power plant, a turbine and an associated condenser, said turbine having superatmospheric and subatmospheric pressure steam bleed points, a boiler for supplying steam to drive the turbine, a conduit through which combustion supporting air is carried into the boiler, conducting means through which the combustion products are conducted from the boiler, a heater receiving exhaust steam from a subatmospheric pressure bleed of the turbine, another heater receiving exhaust steam from the superatmospheric pressure bleed of the turbine, an economizer located within said combustion products conducting means, and a water pipe line extending from the condenser to a heat exchanging element in the first mentioned heater, then to the economizer, then to a heat 4 exchanging element within the second mentioned heater, and then into the boiler.

3. A power plant according to claim 2, wherein an economizer is interposed in a portion of the feed water pipe line within the boiler in advance of the discharge end of said line.

4. A power plant, according to claim 2, further including a water-to-air heating element within the air conduit, a closed auxiliary water circulating pipe line which passes through the first mentioned heater and through the water-to-air heating element, a circulating pump, a valve in said pipe line, and a thermostat within the air conduit connected for automatically controlling said valve in response to the air temperature.

5. In a steam power plant comprising a turbine having a subatmospheric pressure bleed point, a condenser connected to said turbine, a boiler connected to said turbine for supplying steam to drive the turbine, a conduit through which combustion supporting air is carried into the boiler and conducting means through which combustion products are conducted from the boiler; a heater receiving exhaust steam from said bleed point, said heater having two separate coils in heat conducting relation with the steam therein, said coils being entirely free of fluid communication with each other, an economizer located within said combustion products conducting means, a water pipe line extending from the condenser to one of the coils in said heater, then to the economizer and then into the boiler, a water-to-air heating element located within said air conduit, and a closedcircuit water pipe line connected to said water-to-air heating element and to the other coil in said heater, said water pipe lines being free of fluid communication with each other and both in heat exchanging relation with said heater. I

6. The invention set forth in claim 5 characterized in that said conducting means terminates outwardly in a stack preceded by breeching connected thereto, that said economizer is disposed in said breeching in the path of flow of said combustion products, and that the temperature of the exhaust steam in said heater is substantially below the temperature of the combustion products in said breeching.

7. The invention according to claim 6 further characterized in that said conducting means includes an induced draft fan upstream of said economizer.

8. In a steam power plant having a boiler including conducting means for exhausting combustion products terminating outwardly in a stack preceded by breeching connected thereto, a turbine driven by steam from said boiler and a condenser connected to condense steam from said turbine, said turbine having a plurality of steam bleed points of ascending pressures starting with a first bleed point which is below atmospheric pressure and said bleed points being connected to respective feedwater heaters having water coils, the combination which comprises a low level economizer located in said breeching in the path of flow of said combustion products, a feedwater pipe line extending from the condenser to the coil of the heater connected to said first bleed point, then to said economizer, then through the coils of the remaining heaters in series in sequence of ascending bleed point pressures and then to the boiler.

9. The invention according to claim 8 characterized in that said means for exhausting combustion products includes an induced draft fan upstream of said economizer in the path of flow of said combustion products.

10. In a steam power generating system including a boiler having an air intake means, a turbine driven by steam from said boiler, and a condenser connected to condense the steam from said turbine, said turbine having a plurality of steam bleed points of which at least one is below atmospheric pressure, the combination which comprises a subatmospheric pressure feedwater heater, means for carrying steam from said bleed point below atmospheric pressure to said feedwater heater, a low level economizer located in the path of flow of the boiler exhaust gases, means for pumping the condensed steam from the condenser through said feedwater heater and then at a pressure above atmospheric pressure through said low level economizer, and an air preheater arranged in the path of flow of said exhaust gases to transfer heat from said exhaust gases to the incoming air, said low level economizer being downstream with respect to said air preheater.

11. The system defined in claim 10, wherein a blower is located in the exhaust gas stream, and wherein said low level economizer is downstream of said blower and said air preheater is upstream of said blower.

12. The system defined in claim 11, wherein an economizer is located in said exhaust gas stream, upstream of said air preheater.

13. In a steam power generating system including a boiler having an air intake means, a heat exchanger connected in heat exchanging relationship to said air intake means, a turbine driven by steam from said boiler, said turbine having a plurality of steam bleed points of which at least one is below atmospheric pressure, the combination which comprises means for bleeding steam from the turbine bleed point which is below atmospheric pressure, means forming a second heat exchanger connected to said bleeding means, a water conductor extending into said second mentioned heat exchanger for indirect heat exchange with the steam bled from said turbine and extending into said first mentioned heat exchanger, circulating means for circulating the water in said conductor at a pressure above atmospheric pressure for heat exchange with the air in said intake means, flow controlling means arranged to control the flow within said water conductor, and control means having a temperature responsive element arranged in thermal communication with said intake air and connected to said flow controlling means to control the flow of water in response to the temperature of the air.

14. In a steam power plant having a boiler including conducting means for exhausting combustion products terminating outwardly in a stack, a turbine driven by steam from said boiler and a condenser connected to condense steam from said turbine, said turbine having a plurality of steam bleed points of ascending pressures starting with a first bleed point which is below atmospheric pressure and said bleed points being connected to respective feedwater heaters having water coils, the combination which comprises a low'level economizer located in the path of flow of such combustion products, a feedwater pipe line extending from the condenser to the coil of the heater connected to said first bleed point, then to said economizer, then through the coils of the remaining coils in series in sequence of ascending bleed point prasures and then to the boiler.

References Cited in the file of this patent UNITED STATES PATENTS 1,944,059 Baumann Jan. 16, 1934 2,653,447 Heller Sept. 29, 1953 FOREIGN PATENTS 636,923 Great Britain May 10, 1950 931,632 France Feb. 27, 1948 

